Criminal courts across England and Wales will be disrupted for half a day next month when thousands of solicitors join barristers in a mass walkout over government plans to cut legal aid fees by up to 30%.

Opposition within the legal profession to the justice secretary, Chris Grayling, has hardened into coordinated, direct action aimed at forcing him into a last minute rethink of proposals aimed at saving £220m a year.

The involvement of criminal solicitors will spread the disruption beyond crown courts into magistrates courts at the start of the first full working week after the Christmas and new year holidays. Their participation is also likely to ensure the action is more widely observed.

Solicitors, like the CBA, have been careful to avoid describing the protest as a 'strike' because that would raise complex questions over contractual obligations to the Legal Aid Agency.

The decision to take part follows a vote at a meeting of criminal defence solicitors' firms in Birmingham on Thursday. The walkout is designed to highlight the damage they believe will be inflicted on the justice system by fee cuts of between 17.5% and 30%. The LCCSA claims some of the fee changes provide perverse incentives for guilty pleas.

As questions about competitive-tendering and defendants' choice of solicitor have dropped out of the Ministry of Justice's reform package, the dispute has come down simply to fee levels.

Nicola Hill, president of the LCCSA, said: "Solicitors don't take this action lightly. A very short period of disruption should serve as a wake-up call. These cuts aren't just about the legal profession. Far from it.

"These new fees will see cut-price, often inadequate legal advice being dispensed to people whose liberty is at stake and trials collapsing because of poor representation. We're on a slippery slope towards a justice system which sees more innocent people going to jail and the guilty walking free. Reluctantly, like barristers, we've been driven to this."

Bill Waddington, chair of the CLSA, said: "The morning of 6 January is a glimpse into the future of the criminal justice system under the proposals, with a shortage of suitable representation for those who need it. Rightly, our system is the envy of the world. If these plans go through it'll become an international laughing stock."

There is scant public sympathy for lawyers because the stereotype of legal fatcats is so deeply imprinted on the popular imagination. The predicament of those dependent solely on legal aid has been obscured by the rocketing, private legal fees – of allegedly up to £850 an hour – charged by leading solicitors dealing with commercial cases in the City.

A spokesperson for the Law Society, which represents solicitors in England and Wales, said: "There are still battles to be won on behalf of our criminal practitioners, including maximising the number of duty solicitor contracts, dropping the 'single fee – whatever the plea' proposal and maximising opportunities on consortia.

"We're continuing to lobby the government with evidence showing the havoc their proposals will wreak on access to justice and the careers of those who, despite meagre rewards, work hard to provide legal advice and representation in our police stations and courts. We have already secured some key improvements to the government's original plans, which we would not have gained if we had campaigned solely on outright opposition. "

An MoJ spokesperson said: "At around £2bn a year we have one of the most expensive legal aid systems in the world. Just like many hard-pressed families and businesses – we have no choice but to make savings.

"Any disruption to court business is unnecessary, and lawyers choosing to do so inconvenience their clients and hard-working taxpayers. The [MoJ, Legal Aid Agency and courts service] will work together and take all steps possible to minimise the upset this could cause for victims, witnesses and other court users."

"Barristers in Very High Cost Cases (VHCCs) are well-rewarded - around two thirds receive fee incomes of more than £100,000, and often well-over that. Even after our changes they would continue to be generously paid - for both this work and more general crown court work. We have engaged constructively and consistently with lawyers - including revising some proposals in response to their comments - and continue to do so."